1. Field of the Invention
The present invention relates to a vehicle approach warning system, a portable warning terminal, and an in-vehicle communication apparatus.
2. Description of Related Art
Japanese Unexamined Patent Application Publication No. 2007-182195 discloses an alarm system that enables a hearing-impaired person to notice the presence of an alarm horn sound when a vehicle emits the alarm horn sound. Specifically, when the vehicle emits the alarm horn sound, an in-vehicle communication apparatus transmits a warning radio wave to the surroundings. When a portable warning terminal carried by the hearing-impaired person receives this warning radio wave, the portable warning terminal vibrates a vibrator or emits warning-colored light.
The inventors of the present application have found out the followings. A situation requiring a person to be warned is not limited to only a time when a vehicle sounds an alarm horn. For example, when a vehicle approaches a person from his or her back, the person may not notice the approach of the vehicle if the person is hearing-impaired or if the traveling sound of the vehicle is small. In this situation, a driver of the vehicle possibly assumes that the person is noticing the traveling sound of the vehicle and is walking with care. The driver may not sound an alarm horn.